(a) Field of the Invention
The present invention relates to a positioning method and apparatus using a wireless signal, and more particularly, to a positioning method and apparatus used to calculate a location of a terminal by measuring phase differences between wireless signals having periods received from three or more base stations adjacent to a terminal.
(b) Description of the Related Art
In general, methods for enhancing precision of satellite navigation technologies such as the global positioning system (GPS) and the like include differential GPS, a positioning method using a GPS carrier phase, and the like.
The D-GPS, a method of correcting a GPS signal error generated due to diffraction of the atmosphere, an abnormality of a satellite orbit, and the like, is known to improve an error level by up to a 1-meter level in good conditions. However, in an environment in which line-of-sight (LOS) with respect to a satellite is not guaranteed, such as a downtown area, an indoor area, or a mountainous area, an error range increases due to an effect such as delay spread due to multiple paths.
A GPS broadcast wave phase scheme (or RealTime Kinematics (RTK) method), which calculates the number of wavelengths of a satellite carrier signal ranging from 1.5 GHz to 2 GHz and a phase difference, significantly improves positioning precision to a centimeter level. In a GPS carrier phase method, it is important to accurately synchronize a start point at which a positioning terminal and a reference station starts to count wavelengths of simultaneously received satellite carriers, and here, if the positioning terminal moves at a fast speed or if a satellite signal is temporarily blocked by a nearby obstacle or interfered with by slight noise, a phase slip phenomenon in which the number of wavelengths counted by the positioning terminal is different from that of the reference station occurs, causing a positioning error. In this case, the positioning terminal should again start a phase tracking synchronization process with respect to the reference station from scratch.
Meanwhile, in a method of performing positioning using a ground mobile communication base station signal, without relying on the GPS, position coordinates of a positioning terminal are calculated using a cell ID or using a time difference of arrival of signals between a base station and the positioning terminal, and as such, a technique such as observed time difference of arrival (OTDOA) or the like has been known. However, with the positioning methods based on a ground mobile communication base station signal, time synchronization precision between base stations is inferior to that of GPS satellites supporting precise time synchronization by an atomic clock, or the like, and a positioning error of a few meters to tens of meters or greater occurs due to limitations in a bandwidth, a sampling time interval, and the like, of a general broadband mobile communication wireless system.
In order to reduce the error limitations of the ground mobile communication base station-based positioning methods, a positioning method based on a phase measurement of a reception signal in a wireless communication network has been proposed. In this method, a positioning terminal calculates phase rotation values of time-synchronized OFDM preamble signals from three or more adjacent base stations, and obtains absolute coordinate values thereof by using differences in the phase rotation values of the three or more base stations and differences in distances converted therefrom.
In the positioning method based on phase measurement of a reception signal, since continuous rotation values of a signal phase are used, a time error due to discretized sampling is reduced and more precise time resolving power (or resolution) can be obtained. However, the positioning method fails to improve precision beyond a theoretical sampling time interval limitation, i.e., a bandwidth limitation, and does not provide a method for reducing an error occurring when base stations are not synchronized in time.
In general, mobile communication base station systems perform time synchronization based on GPS satellite signals, and in this case, a synchronization error of nanoseconds (ns) or greater may occur on the ground. A resultant positioning error may be a few meters or greater.
Also, in the foregoing positioning methods based on satellite and ground base station signals, when positioning is performed in a downtown area or a mountainous area, a signal is subjected to reflection and diffraction with a nearby building or obstacle and reach through various paths. In this case, when a position is calculated on the basis of the reflected or diffracted signal, the calculated position may be different from an actual position, and the resultant positioning error may range from a few meters to tens of meters. Thus, the related art positioning methods based on satellites and base stations generally have a severe positioning error in a downtown area or in a mountainous area or cannot be used in an indoor area.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.